I think it could be the same issue as I had, my headphones would take ages to be recognised or sometimes not at all until eventually they were never detected. The problem was that the headphone jack is connected electrically to the motherboard using sprung contacts, this is a good design as you can never break the headphone socket by yanking on the headphone lead which happens time to time by mistake. But, over time the contacts got dirty due to sweat, moisture, all I had to do was strip the handset down, clean and tweak the contacts to have a little more pressure and it was fixed . I found a N900 strip down on youtube and carefully followed it,

I think it could be the same issue as I had, my headphones would take ages to be recognised or sometimes not at all until eventually they were never detected. The problem was that the headphone jack is connected electrically to the motherboard using sprung contacts, this is a good design as you can never break the headphone socket by yanking on the headphone lead which happens time to time by mistake. But, over time the contacts got dirty due to sweat, moisture, all I had to do was strip the handset down, clean and tweak the contacts to have a little more pressure and it was fixed . I found a N900 strip down on youtube and carefully followed it,

J

hai, thank for a respond
i just finished disassembly, every part of this phone, and doing some tweak to headphone jack contact but it seem no luck.

but if i plug-in in using another headphone or any active speaker, phone eagerly can detect it.

I think it could be the same issue as I had, my headphones would take ages to be recognised or sometimes not at all until eventually they were never detected. The problem was that the headphone jack is connected electrically to the motherboard using sprung contacts, this is a good design as you can never break the headphone socket by yanking on the headphone lead which happens time to time by mistake. But, over time the contacts got dirty due to sweat, moisture, all I had to do was strip the handset down, clean and tweak the contacts to have a little more pressure and it was fixed . I found a N900 strip down on youtube and carefully followed it,

J

Might be coming late to the party but that fixed my problem of wonky headphone jack on my second N900
Some dirt accumulated inside the jack en the pins where almost flat after 5+ years. Cleaned it, bent the pins back up and my jack is flawless again